This invention relates generally to valve gated injection molding apparatus and more particularly to such apparatus having three position valve member actuating mechanism for multi-layer molding.
Valve gated injection molding apparatus for making multi-layered protective containers for food or preforms or parisons for beverage bottles are well known. Often the inner and outer layers are made of a polyethylene terephthalate (PET) type material with one or more barrier layers made of a material such as ethylene vinyl alcohol copolymer (EVOH) or nylon. For instance, U.S. Pat. No. 4,657,496 to Ozeki et al. which issued Apr. 14, 1987 shows an actuating mechanism having an outer piston reciprocating in an outer cylinder and an inner piston reciprocating in an inner cylinder. The inner piston drives the elongated valve member and the outer piston drives a stem surrounding the elongated valve member and they operate in a controlled injection cycle to sequentially inject first the PET and then the barrier material to mold three layer products. While this is satisfactory for some applications, sequential molding has the disadvantage of a relatively lengthy cycle time.
As seen in U.S. Pat. No. 4,919,606 to Gellert which issued Apr. 24, 1990, rack and pinion valve member actuating mechanism is also known. However, previously it had the disadvantage of only providing open and closed positions, which is not sufficient for multi-layer molding.